Revert PR #124400 runtime-async crossgen outerloop test leg

[Copilot]

Since runtime async is now enabled by default, we no longer need to explicitly enable it in a separate pipeline job.

This PR prepares a clean revert of PR #124400 by removing the runtime-async crossgen libraries test leg from main while keeping later unrelated pipeline/test-infra changes intact.

• Scope

  • Reverts the TestReadyToRun_RuntimeAsync_Libraries leg added to eng/pipelines/coreclr/crossgen2.yml.
  • Leaves subsequent changes in eng/testing/tests.targets untouched (they are newer, independent behavior updates beyond Add legs to run crossgenned libraries tests with runtime-async enabled #124400).

• Net effect

  • Stops running the dedicated TestReadyToRun + UseRuntimeAsync=true libraries matrix in the runtime-coreclr crossgen pipeline.
  • Preserves existing non-runtime-async crossgen test legs and all other pipeline structure.

# removed from eng/pipelines/coreclr/crossgen2.yml
buildArgs: -s clr+libs+libs.tests
           -c $(_BuildConfig)
           /p:TestReadyToRun=true
           /p:UseRuntimeAsync=true
           /p:ArchiveTests=true
nameSuffix: TestReadyToRun_RuntimeAsync_Libraries

Original prompt

Create a branch on the user's fork of dotnet/runtime and prepare a revert of the PR identified earlier in the conversation: #124400 ("Add legs to run crossgenned libraries tests with runtime-async enabled").

Requirements:

• Work in repository dotnet/runtime.
• Use base branch main.
• Create a new branch on the user's fork for the revert work.
• Revert the changes introduced by PR Add legs to run crossgenned libraries tests with runtime-async enabled #124400 as cleanly as possible.
• If a direct revert is not possible, make the branch contain the safest minimal changes to undo the effect of the PR while preserving unrelated changes.
• Ensure the branch is ready for review with a clear commit message and PR description summarizing what is being reverted and any caveats.

Context from the conversation:

• The user wants to revert the PR that added runtime-async legs to the runtime-coreclr crossgen pipeline.
• The PR previously identified is Add legs to run crossgenned libraries tests with runtime-async enabled #124400.
• The repository and base branch are explicitly provided by the user as dotnet/runtime and main.

The following is the prior conversation context from the user's chat exploration (may be truncated):

User: Can you find my PR that added runtime-async legs to the runtime-coreclr crossgen pipeline?

Assistant: I found a strong match: Add legs to run crossgenned libraries tests with runtime-async enabled.

It says it:

• “Adds legs to the crossgen outerloops to run libraries tests with runtime-async enabled.”

A couple of other close matches from your recent PRs:

• Skip covariant-return test when running crossgen tests
• Add pipeline legs for crossgen2 with --large_version_bubble

Showing 10 of 11 results.
You can view more in GitHub search here:
https://github.com/dotnet/runtime/issues?q=is%3Apr+author%3Ajtschuster+%22runtime-async%22+crossgen

If you want, I can also narrow this down further to the exact PR by:

• state: open/closed
• date range
• label: runtime-async or area-ReadyToRun
• whether it was the PR that added the legs vs. the PR that fixed the underlying async crossgen behavior

User: Can I set up a revert of that PR in the github UI?

Assistant: Yes — if the PR was merged to the upstream branch, GitHub lets you start a revert right in the PR UI.

GitHub docs say:

• A revert in GitHub creates a new pull request that reverts the merge commit from the original PR.
• You need write permissions in the repository.
• On the PR page, you can click Revert near the bottom, then merge the resulting revert PR.
  Source: Reverting a pull request

A couple caveats:

• If the PR wasn’t merged on GitHub or was merged with fast-forward, the UI revert may not be available.
• If the revert causes merge conflicts, you may need to revert commits manually instead.

If you want, I can also help you check whether that specific PR has a Revert button available and what the safest revert path is.

User: Okay, it can't easily be reverted, can you try reverting the commit for me with and creating a branch on my fork?

Assistant: I’m waiting for the result of the branch/revert setup so I can continue.

This pull request was created from Copilot chat.

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[Copilot]

Pull request overview

Removes the dedicated runtime-async crossgen2 libraries test leg from the CoreCLR crossgen2 pipeline, as runtime-async is now enabled by default and the explicit UseRuntimeAsync=true matrix is no longer needed.

Changes:

• Deletes the TestReadyToRun_RuntimeAsync_Libraries platform-matrix job from eng/pipelines/coreclr/crossgen2.yml.
• Keeps the existing non-runtime-async TestReadyToRun_Libraries leg and the rest of the pipeline structure unchanged.